Full text of "Solar energy system performance evaluation : Living systems, Davis, California"

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SOLAR/1046-79/14

FEB 14 1980

Solar Energy System
Performance Evaluation

LIVING SYSTEMS
SINGLE-FAMILY RESIDENCE

Davis, California
October 1978 Through March 1979

U.S. Department of Energy

National Solar Heating and
Cooling Demonstration Program

National Solar Data Program

NOTICE

This report was prepared as an account of work sponsored by the United States
Government. Neither the United States nor the United States Department of Energy, nor
any of their employees, nor any of their contractors, subcontractors, or their employees,
makes any warranty, express or implied, or assumes any legal liability or responsibility for
the accuracy, completeness or usefulness of any information, apparatus, product or process
disclosed, or represents that its use would not infringe privately owned rights.

This report has been reproduced directly from the best available copy.

Available from the National Technical Information Service, U. S. Department of
Commerce, Springfield, Virginia 22161.

Price: Paper Copy $5.25
Microfiche S3.00

SOLAR/1046-79/14

Distribution Category UC-59

SOLAR ENERGY SYSTEM PERFORMANCE EVALUATION

LIVING SYSTEMS
DAVIS, CALIFORNIA

OCTOBER 1978 THROUGH MARCH 1979

I. GRAY KINNIE, PRINCIPAL AUTHOR

JERRY T. SMOK, MANAGER OF RESIDENTIAL SOLAR ANALYSIS

LARRY J. MURPHY, IBM PROGRAM MANAGER

IBM CORPORATION
18100 FREDERICK PIKE
GAITHERSBURG, MARYLAND 20760

PREPARED FOR

THE DEPARTMENT OF ENERGY

OFFICE OF ASSISTANT SECRETARY FOR

CONSERVATION AND SOLAR APPLICATION

UNDER CONTRACT EG-77-C-01-4049

H. JACKSON HALE, PROGRAM MANAGER

TABLE OF CONTENTS

Page

1 . FOREWORD 1-1

2. SUMMARY AND CONCLUSIONS 2-1

2.1 Performance Summary 2-1

2.2 Conclusions 2-1

3. SYSTEM DESCRIPTION 3-1

4. PERFORMANCE EVALUATION TECHNIQUES 4-1

5. PERFORMANCE ASSESSMENT 5-1

5.1 Weather Conditions 5-1

5.2 System Thermal Performance 5-3

5.3 Storage Performance 5-9

5.4 Energy Savings 5-18

6. REFERENCES 6-1

APPENDIX A DEFINITIONS OF PERFORMANCE FACTORS AND SOLAR TERMS A-l

APPENDIX B SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS B-l

APPENDIX C LONG-TERM AVERAGE WEATHER CONDITIONS C-l

LIST OF ILLUSTRATIONS

FIGURES
3-1

3-2
5-1
5-2
5-3
5-4
5-5

5-6

TITLE

Active Solar Domestic Hot Water System
Schematic

Passive Space Heating System

Energy Flow

Average Monthly Storage Temperatures

Average Seasonal Comfort Levels

Slab Storage Gradient vs. Insolation

Slab Temperatures on a North - South Slice
through House

System Performance - January 29-30, 1979

PAGE
3-2

3-3

5-8

5-11

5-13

5-14

5-16

5-17

TABLES
5-1
5-2
53
5-4
5-5

LIST OF TABLES

TITLE
Weather Conditions

Thermal Performance - Heating Season
System Thermal Performance
Storage Performance, Two Sample Days
Energy Savings

PAGE

5-2

5-4

5-6

5-10

5-19

NATIONAL SOLAR DATA PROGRAM REPORTS

Reports prepared for the National Solar Data Program are numbered under speci
fie format. For example, this report for the Living Systems project site
is designated as SOLAR/1046-79/14. The elements of this designation are
explained in the following illustration.

SOLAR/1046-79/14

Prepared for the

National Solar

Data Program

Demonstration Site

Report Type
Designation

Year

o Demonstration Site Number:

Each project site has its own discrete number - 1000 through 1999 for
residential sites and 2000 through 2999 for commercial sites.

Report Type Designation:

This number identifies the type of report, e.g.,

Monthly Performance Reports are designated by the numbers 01 (for
January) through 12 (for December).

Solar Energy System Performance Evaluations are designated by the
number 14.

Solar Project Descriptions are designated by the number 50.

Solar Project Cost Reports are designated by the number 60.

These reports are disseminated through the U. S. Department of Energy Technical
Information Center, P. 0. Box 62, Oak Ridge, Tennessee 37830.

Digitized by the Internet Archive

in 2012 with funding from

University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation

http://archive.org/details/solarliving1979

1 . FOREWORD

The National Program for Solar Heating and Cooling is being conducted by the
Department of Energy under the Solar Heating and Cooling Demonstration Act of
1974. The overall goal of this activity is to accelerate the establishment
of a viable solar energy industry and to stimulate its growth in order to
achieve a substantial reduction in nonrenewable energy resource consumption
through widespread applications of solar heating and cooling technology.

Information gathered through the Demonstration Program is disseminated in a
series of site-specific reports. These reports are issued as appropriate and
may include such topics as:

o Solar Project Description

o Design/Construction Report

o Project Costs

o Maintenance and Reliability

o Operational Experience

o Monthly Performance

o System Performance Evaluation

The International Business Machines Corporation is contributing to the overall
goal of the Demonstration Act by monitoring, analyzing, and reporting the
thermal performance of solar energy systems through analysis of measurements
obtained by the National Solar Data Program.

The Solar Energy System Performance Evaluation Report is a product of the
National Solar Data Program. Reports are issued periodically to document the
results of analysis of specific solar energy system operational performance.
This report includes system description, operational characteristics and
capabilities, and an evaluation of actual versus expected performance. The
Monthly Performance Report, which is the basis for the Solar Energy System
Performance Evaluation Report, is published on a regular basis. Each parameter
presented in these reports as characteristic of system performance represents
over 8,000 discrete measurements obtained each month by the National Solar

1-1

Data Network (NSDN). Documents referenced in this report are listed in
Section 6, "References." Numbers shown in brackets refer to reference numbers
in Section 6.

This Solar Energy System Performance Evaluation Report presents the results
of a thermal performance analysis of the Living Systems solar energy system.
The analysis covers operation of the system from October 1978 through
March 1979. Living Systems solar energy system provides space heating, and
domestic hot water to a single-family dwelling located in Davis, California.
However, only the space heating subsystem will be discussed in this report.
Section 2 presents a summary of the overall system results. A system descrip-
tion is contained in Section 3. Analysis of the system thermal performance
was accomplished using a system energy balance technique described in Section
4. Section 5 presents a detailed assessment of the individual subsystems
applicable to the site.

The measurement data for the reporting period were collected by the NSDN [1].
System performance data are provided through the NSDN via an IBM-developed
Central Data Processing System (CDPS) [2]. The CDPS supports the collection
and analysis of solar data acquired from instrumented systems located through-
out the country. These data are processed daily and summarized into monthly
performance reports. These monthly reports form a common basis for system
evaluation and are the source of the performance data used in this report.

Acknowledgments are extended to those individuals involved in the operation
of the Living Systems solar energy system: Johnathan Hammond, James Plumb,
Brian and Catrina Tarkinson. Their insight and cooperation in the resolution
of various on-site problems during the reporting period were invaluable.

1-2

2. SUMMARY AND CONCLUSIONS

This section provides a summary of the performance of the solar energy system
installed at Living Systems, located in Davis, California for the period
October 1978 through March 1979. This solar energy system is designed to
support the active preheating of domestic hot water and passive space heating
loads; however, only passive space heating is covered in this report. A
detailed description of the Living Systems solar energy system operation is
presented in Section 3.

2.1 Performance Summary

The solar energy site was occupied 5 months of the season from November 1978
through March 1979 and the solar energy system operated continuously during
the entire reporting period. The total incident solar energy was 54.41 million
Btu, of which 21.80 million Btu was collected by the solar energy system.
Wood, another renewable resource, provided 4.65 million Btu toward the space
heating load. Solar energy satisfied 79 percent of the space heating require-
ments. The solar energy system provided fossil fuel savings of 37.18 million
Btu.

This performance level is reasonably close to the expected design performance;
the differences in expected and actual performance can be accounted for by
both the severe winter weather conditions encountered and by facets of owner
interaction with the operation of the system. Some minor items are expected
to be completed before next winter, after which the house should exceed its
previous performance.

Comfort levels in the major portions of the building were acceptable all
season, but early morning chill was occasionally experienced in the bedrooms.
The relative humidity was \/ery stable from day to day.

2.2 Conclusions

The Living Systems site has proven the concepts and received enthusiastic
acceptance from the owners. The site was an early model. Subsequent systems

2-1

developed by the designers use passive hot water preheat systems, slab edge
insulation and alternate methods for water tube anchoring. The primary
backup heat system was a small, natural convection, natural gas heater; it
was not used after February 18, 1979. For this reason, solar energy replaced
79 percent of the heat that would have been required from natural gas, a
nonrenewable resource. In addition, the owners bought two cords of wood for
the wood stove, but used only one third of a cord. Weather-stripping the two
rear doors and completing the anchoring of the insulating curtains should
provide better performance next year.

2-2

3. SYSTEM DESCRIPTION

The Living Systems site is a single-family residence in Davis, California.
The home has approximately 1700 square feet of conditioned space. The solar
energy system consists of two independently-controlled systems: an active
system for preheating domestic-hot-water (DHW) and a passive system for space
heating the home.

The active solar DHW system has an array of flat-plate collectors with a
gross area of 46 square feet. The array faces south at an angle of 45
degrees to the horizontal. Potable city water is the transfer medium used
throughout the system. In the event of freezing and no insolation, the con-
troller drains the water from the collectors. When water in the collector is
sufficiently warmer than the water in the preheat storage tank, the controller
starts the circulation between the preheat tank and the collector. The preheat
tank holds 82 gallons of water which is supplied, on demand, to a conventional
20-gallon DHW tank. When the water preheated by solar energy is not hot
enough to satisfy the hot water load, a natural gas burner in the DHW tank
provides auxiliary energy for water heating. The system is shown schematically
in Figure 3-1 .

The passive solar space heating system is of the direct-gain type illus-
trated schematically in Figure 3-2. Incident solar energy is admitted to the
building through both the large south-facing vertical windows (approximately
200 square feet) and the overhead skylight (approximately 80 square feet with
a tilt of 60 degrees to the horizontal). Manually-operated insulating curtains
provide insulation during the night and sunless days for the south-facing
collector windows. Manually-operated insulating shutters also provide night
insulation for the skylight glazing and are aluminum-coated to provide reflec-
tion to the space below when open. Solar energy is stored in steel tubes
that contain approximately 3600 gallons of water. The tubes are painted blue
and placed near the south window wall and under the skylight. Additional
storage is provided by the 6-inch-thick concrete slab floor of the building
which is covered by brown ceramic tile. Collected solar energy is distributed

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by natural convection, by conduction through the slab floor, and by radiation.
Floor covering is minimal: linoleum in the kitchen and eating area and white
shag rugs in two bedrooms. The building envelope is well insulated in order
to ensure energy conservation, with R-19 insulation in the walls and R-30
insulation in the roof. The effective R-values of the windows are in the
range of R-2 to R-10 (uncovered and covered with curtains and shutters). All
glass surfaces are double-glazed with minimum window area in nonsouth-facing
walls. Auxiliary space heating is provided by a gas-fired wall furnace which
distributes the energy by natural convection. Additional auxiliary energy can
be supplied from a wood-burning stove.

3-4

4. PERFORMANCE EVALUATION TECHNIQUES

The performance of the Living Systems solar energy system is evaluated by
calculating a set of primary performance factors which are based on those
proposed in the intergovernmental agency report "Thermal Data Requirements
and Performance Evaluation Procedures for the National Solar Heating and
Cooling Demonstration Program" [3]. These performance factors quantify the
thermal performance of the system by measuring the amount of energies that
are being transferred between the components of the system. The performance
of the system can then be evaluated based on the efficiency of the system in
transferring these energies. A list of all performance factors and their
definitions are listed in Appendix A.

Data from monitoring instrumentation located at key points within the solar
energy system are collected by the National Solar Data Network. This data is
first formed into factors showing the hourly performance of each system com-
ponent, either by summation or averaging techniques, as appropriate. The
hourly factors then serve as a basis for the calculation of the daily and
monthly performance of each component subsystem. The analysis technique used
is outlined in the report, "Performance Evaluation Reporting for Passive
Systems" [4]. The performance factor equations for this site are listed in
Appendix B.

Each month, as appropriate, a summary of overall performance of the Living
Systems site and a detailed subsystem analysis is published. These monthly
reports for the period covered by this Solar Energy System Performance Evalua-
tion (October 1978 through March 1979) are available from the Technical
Information Center, Oak Ridge, Tennessee 37830.

In the tables and figures in this report, an asterisk indicates that the
value is not available for that month; N.A. indicates that the value is not
applicable for this site.

4-1

5. PERFORMANCE ASSESSMENT

The performance of the Living Systems solar energy system has been evaluated
for the October 1978 through March 1979 time period. Two perspectives were
taken in this assessment: The first views the overall system in which the
total solar energy collected, the system load, the measured values for solar
energy used, and system solar fraction are presented. The second examines
(in Section 5.4) the equivalent energy savings contributed by the solar
energy system.

The performance assessment of any solar energy system is highly dependent on
the prevailing weather conditions at the site during the period of performance,
The original design of the system is generally based on the long-term averages
for available insolation and temperature. Deviations from these long-term
averages can significantly affect the performance of the system. Therefore,
before beginning the discussion of actual system performance, a presentation
of the measured and long-term averages for critical weather parameters has
been provided.

5.1 Weather Conditions

Monthly values of the total solar energy incident in the plane of the col-
lector array and the average outdoor temperature measured at the Living
Systems site during the reporting period are presented in Table 5-1. Also
presented in Table 5-1 are the corresponding long-term average monthly values
of the measured weather parameters. These data are taken from Reference
Monthly Environmental Data for Systems in the National Solar Data Network [4].
A complete yearly listing of these values for the site is given in Appendix C.

During October 1978 through March 1979, the average daily total incident solar
energy on the collector window was 1095 Btu per square foot per day. This is
below the estimated average daily solar radiation for this geographical area
during the reporting period of 1176 Btu per square foot per day for a south-
facing plane with a tilt of 60 degrees to the horizontal. The average ambient

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temperature from October 1978 through March 1979 was 50°F as compared with
the long-term average of 52°F from October through March. The number of
heating degree-days for the same period (based on a 65°F reference) was 2978,
as compared with the long-term average of 2471.

Monthly values of heating degree-days are derived from daily values of ambient
temperature and are useful indications of the system heating loads. Heating
degree-days are computed as the difference between daily average temperature
and 65°F. For example, if a day's average temperature was 60°F, then five
heating degree-days are accumulated. The total number of heating degree-days
is summed monthly.

Daily analysis of wind speeds for the period shows that frequent peaks occurred
which exceeded a 10 mph daily average with one peak at 18 and another at
22 mph. Similar analysis of outdoor relative humidities indicated that
"cold-dry" days are almost nonexistent in Davis, California. Only during the
warmer days of October were there days with low humidity.

Analysis of the weather conditions for the months November 1978 through
March 1979 shows that winter was more severe than the long-term average: the
incident solar energy was less, the temperature was lower and the resultant
heating degree-days higher.

5.2 System Thermal Performance

The thermal performance of a solar energy system is a function of the total
solar energy collected and applied to the system load. The total system load
is the sum of the solar and auxiliary thermal energies delivered to the loads
(excluding losses in the system). The portion of the total load supported by
solar energy is defined as the solar fraction of the load.

The thermal performance of the Living Systems solar energy system is presented
in Table 5-2. This performance assessment is based on the 6-month period
from October 1978 to March 1979. During the reporting period, a total of

5-3

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21.80 million Btu of solar energy was collected, a total of 22.33 million Btu
of solar energy was used, and the total system load for space heating was
28.30 million Btu. The discrepancy between solar energy used and solar
energy collected is the excess heat available in storage at the beginning of
November 1978. The measured system solar fraction was 79 percent as compared
to an expected value of 88 percent for the winter season.

In Table 5-1, note that the number of heating degree-days for November and
December considerably exceeded the long-term average, but January had fewer
heating degree-days than the long-term average. In Table 5-2, the heating
load was highest in December rather than in January (as suggested by the long-
term heating degree-day column in Table 5-1). The December weather was colder
than January; the December insolation was also considerably lower than expected.
Over the Christmas holidays, the relatively new wood stove overheated, causing
the occupants to open windows and vent, and to operate the fan for several
hours. Unfortunately, the vent remained open for several days, increasing the
space heating load considerably. This emphasizes the cooperation required of
the occupants of a passive home. By late January, the new owners (since
November 1) were using minimum auxiliary, nonrenewable fossil fuel for heat.
The last time fossil fuel was used was on February 18; the pilot light was
turned off on March 4 to save energy.

Table 5-3 contains additional information on thermal performance: The wood
stove, using a renewable resource, reduced the apparent space heating load of
the home. In October, the house was sometimes in the summer mode and sometimes
heated by a part-time caretaker. In December, the wood stove was not used as
often as in the other cold months and aggravated the severe weather load on
the home.

A total of 4.65 million Btu of auxiliary thermal energy was derived from use
of the wood stove during the winter. According to the occupants, approximately
one third of a cord of wood was used during the winter. Assuming a heat
content of 30 million Btu per cord of wood, the wood stove provided energy at
an average efficiency level of 47 percent. However, the sample size was too
small to put much credence in this figure. The wood stove was used primarily

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to maintain a lower bound to the building temperature and interior comfort
level. Therefore, the wood stove was used mostly at night and through the
early morning and on cloudy days.

In order to satisfy the building load, additional energy was derived from
electric lights, appliances, etc. External lights for the yard, entryways,
and garage did not contribute.

For reporting purposes, the reported load is an equivalent equipment demand.
As illustrated in Table 5-3, this space heating equipment demand is the
difference between the building load and the wood energy gains. This demand
is the amount of energy which would be required to maintain the measured
building environmental conditions. Approximately 79 percent of this space
heating subsystem demand was satisfied by collected solar energy. Only 5.97
million Btu of auxiliary fossil fuel (natural gas) was used over the entire
heating season.

One more observation should be made from this table: While the external
relative humidity was rather high, the internal relative humidity was stable
near the bottom of the comfort zone. The occupants, however, have indicated
complete comfort with this low relative humidity.

The primary collection of incident solar energy at the Living Systems site
occurs through the south-facing windows and skylight and goes directly to
the water tube and concrete storage. Energy stored in the form of heated
water or heated concrete is transferred to the air in the house by conduction
and convection. This is shown graphically in Figure 5-1. The solar energy
collection efficiency reaches a maximum near the coldest part of the year
(mid-winter) and drops off rapidly in the fall and spring when there is
relaxation of the rigid schedule of opening and closing insulating shutters
and curtains, and when shading and venting to control overheating reduces
the efficiency of energy collection. It is of particular interest to compare
the conversion efficiencies of January, February, and March 1979: 70 percent,
54 percent, and 40 percent, respectively. It should be noted that the value

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of collection efficiency does not directly compare to the collection effi-
ciencies presented for active solar energy systems, because the thermal
losses that occur through the passive system glazing are a part of the
building load instead of a part of the collection efficiency.

5.3 Storage Performance

Primary storage of collected solar energy at the Living Systems site is
provided by the concrete slab floors of the building and the south and central
water tubes. Evidence indicates that the gravel and earth below the slab
provide additional storage (about twice the size of the slab). This storage
would be even larger if the early version of the Living Systems homes had
been constructed with slab-edge insulation as are the newer models.

To compare the effectiveness of three storage areas, two contrasting days in
January were selected: one with no insolation and one with very high insola-
tion. In Table 5-4, on January 7, 1979, when the sun did not shine, the
central and south water tubes experienced about the same temperature drop.
However, the slab was the primary source of heating for the rear bedrooms.
The conclusion is that the slab and sub-slab have large storage capacity and
are more stable. On January 22, 1979, when the sun was at its hottest, the
central water tubes had the largest temperature rise and the slab actually
lost temperature. This loss reflects the continued drain from earlier days.
The conclusion is that the water tubes are better collectors, while the slab
is more involved in satisfying the space heating distribution. For this
reason, as well as the problem with edge insulation, the average slab tempera-
ture remains considerably below the water tube temperature. The seasonal
view is shown in Figure 5-2. The water tube temperature is always several
degrees above the slab temperature with the average temperature somewhere
between them. In this plot, the three storage areas are averaged equally.
Had weighted averaging based on the thermal capacity been used, the building
storage temperature would be somewhat lower.

Notice also that except in March when some very warm days were experienced,
the average building temperature was always below the storage temperature.

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5-11

Fresh air enters this building primarily through infiltration. The cool
outside air is heated by the energy stored in the water tubes and slab.
Thus, the building temperature stays below the average storage temperature
all winter. A clearer picture of this is apparent in Figure 5-3. Note that
calculated comfort levels in zone 1, the front half of the building, and in
zone 2, the bedrooms and master bath, are always higher than the building
temperature.

The comfort index used in this analysis is the operative temperature, which
is defined as the average of the space dry bulb and mean radiant temperatures.
For this analysis, the space mean radiant temperature is defined as the
average surface temperature of all radiating surfaces bordering the space,
except for the wood stove, since a surface temperature measurement of the
wood stove was available for only a small portion of the season. The building
is divided into two comfort zones: Zone 1 is the south part of the building,
while zone 2 is the north part of the building. While relative humidity does
play an important part in the perception of comfort, it is not presently
included in the comfort index. Comfort levels in zone 2 were occasionally
below those that would be acceptable for some individuals, but the owners are
conservation conscious and accepted them. Comfort levels in zone 1 were
normally acceptable. The occupants verified these observations.

The earth around cellars can be used to keep them cool because the earth
remains at 52 to 57°F year-round. However, when a warm surface such as a
slab is placed on top of the earth, the thermal lag of the earth prevents
rapid dissipation of the heat to the cooler subsurface. A volume of the
earth under the slab acts as additional storage, moderating the heat of the
house. In the Living Systems site, two sets of three sensors each were
positioned to measure the temperature gradient across the slab storage: one
sensor was placed one inch below the slab surface, one at six inches below
the top of the slab and another at 11 inches below the top of the slab into
the earth below the gravel. Figure 5-4 shows the plotted temperature values
at these three locations together with a plot of the insolation values on a
sunny January day. With sensors of this type, absolute values should not be
considered; the shapes of the curves are of interest. As the sun came out,

5-12

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5-14

the slab surface started to heat almost immediately, the middle was delayed
about two hours and the bottom was delayed about six hours. Although none of
the areas of the slab were in the uncomfortable range at any time, the tem-
perature swing on the top surface was about 5°F; whereas the temperature
swing in the earth was only about 0.8°F.

Taking another viewpoint, the Living Systems site is instrumented so that
temperatures on a north-south slice through the house can be measured.
Figure 5-5 shows temperatures one inch below the slab surface at 0800 (8 a.m.)
and 1600 (4 p.m.) on the same day as the previous figure. The small water
tanks moderate the edge temperature in the front, but also shade the front
area of the slab. The large and small water tubes and front slab keep the
largest part of the house warm. However, behind the partition, the tempera-
ture drops rapidly toward the back wall. During this period, the rear center
room shown on this chart was the coldest bedroom because of an open ceiling
access. However, adjacent room slabs were almost only a few degrees warmer.
As mentioned earlier, these homes now have edge insulation and this drop
should be considerably less.

With the aid of Figure 5-6, one can review typical operation of the Living
Systems home over a two-day, January period; one day was sunny, the other
mostly cloudy. In the early hours of January 29, 1979, the outside tempera-
ture was below freezing and dropping. Storage and inside temperatures were
also dropping with inside temperature somewhat chilly. Around 5 a.m. the gas
heater came on and the building temperature started to rise. As the sun came
up, the occupants opened the insulating shutters and curtains. The ceiling
Casablanca fan was turned on for a little over an hour. During winter use,
this fan distributes hot air which has risen, both naturally and from the
heater; the fan also abstracts some heated air from the large water tubes.
During the day, both storage and building temperatures rose. As the sun went
down, the shutters and curtains were manually closed and the fan was turned
on for almost an hour. The gas heater operated for short bursts through the
evening and night and for two hours in the early morning. The shutters and
curtains were opened during the short period when the sun was shining and

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JANUARY 29

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TIME OF DAY (HOURS)

12
JANUARY 30

Figure 5-6. SYSTEM PERFORMANCE - JANUARY 29-30, 1979

LIVING SYSTEMS
5-17

some heat was gained. The wood stove was fired up from about noon until 5 p.m.
and the fan was subsequently turned on. The storage and building temperatures
were both higher at the end of the two-day period. Shutters, curtains, fan,
wood stove and possibly the thermostat (not instrumented) were operated
manually during the two-day period.

5.4 Energy Savings

Energy savings for the reporting period are presented in Table 5-5. The
total savings were 37.18 million Btu, for a monthly average of 6.20 million
Btu.

Solar energy system savings are realized whenever energy provided by the
solar energy system is used to meet system demands which would otherwise be
met by auxiliary energy sources.

5-18

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6. REFERENCES

1. U.S. Department of Energy, National Solar Data Network , prepared
under contract number EG-77-C-4049 by IBM Corporation,
December 1977.

2. J. T. Smok, V. S. Sohoni , J. M. Nash, "Processing of Instrumented
Data for the National Solar Heating and Cooling Demonstration
Program," Conference on Performance Monitoring Techniques for
Evaluation of Solar Heating and Cooling Systems, Washington, D.C.,
April 1978.

3. E. Streed, et. al . , Thermal Data Requirements and Performance
Evaluation Procedures for the National Solar Heating and Cooling
Demonstration Program , NBSIR-76-1137, National Bureau of Standards
Washington, D.C. , 1976.

4. "Performance Evaluation Reporting for Passive Systems", April 17,
1979, SOLAR/0018-79/35.

5. "A Thermal Performance Analysis Technique for Passive Solar Space
Heating Systems" proceedings of the 3rd National Passive Solar
Conference, January 11-13, 1979, San Jose, California.

6. Mears, J. C. Reference Monthly Environmental Data for Systems in
the National Solar Data Network . Department of Energy report
SOLAR/0019-79/36. Washington, D.C, 1979.

1 A Monthly Performance Report , Living Systems , SOLAR/1024-78/10,
Washington, D.C, Department of Energy (October 1978).

8.# Monthly Performance Report , Living Systems , SOLAR/1046-78/1 1 ,
Washington, D.C, Department of Energy (November 1978).

9.# Monthly Performance Report , Living Systems , SOLAR/1046-78/12,
Washington, D.C, Department of Energy (December 1978).

10. # Monthly Performance Report , Living Systems , SOLAR/1046-79/01,
Washington, D.C, Department of Energy (January 1979).

ll.# Monthly Performance Report , Living Systems , SOLAR/1046-79/02,
Washington, D.C, Department of Energy (February 1979).

12. # Monthly Performance Report , Living Systems , SOLAR/1046-79/03,
Washington, D.C, Department of Energy (March 1979).

13.# "Users' Guide to the Monthly Performance Report of the National
Solar Data Program," February 28, 1978, SOLAR/0004-78/18.

#Copies of these reports may be obtained from Technical Information Center,
P. 0. Box 62, Oak Ridge, Tennessee 37830.

6-1

APPENDIX A
DEFINITIONS OF PERFORMANCE FACTORS AND SOLAR TERMS

COLLECTOR ARRAY PERFORMANCE

The collector array performance is characterized by the amount of solar
energy collected with respect to the energy available to be collected.

o INCIDENT SOLAR ENERGY (SEA) is the total insolation available
on the gross collector array area. This is the area of the
collector array energy-receiving aperture, including the
framework which is an integral part of the collector structure.

o OPERATIONAL INCIDENT ENERGY (SEOP) is the amount of solar energy
incident on the collector array during the time that the col-
lector loop is active (attempting to collect energy).

o COLLECTED SOLAR ENERGY (SECA) is the thermal energy removed
from the collector array by the energy transport medium.

o COLLECTOR ARRAY EFFICIENCY (CAREF) is the ratio of the energy
collected to the total solar energy incident on the collector
array. It should be emphasized that this efficiency factor is
for the collector array, and available energy includes the
energy incident on the array when the collector loop is inac-
tive. This efficiency must not be confused with the more
common collector efficiency figures which are determined from
instantaneous test data obtained during steady-state operation
of a single collector unit. These efficiency figures are often
provided by collector manufacturers or presented in technical
journals to characterize the functional capability of a partic-
ular collector design. In general, the collector panel maximum
efficiency factor will be significantly higher than the col-
lector array efficiency reported here.

STORAGE PERFORMANCE

The storage performance is characterized by the relationships among the
energy delivered to storage, removed from storage, and the subsequent
change in the amount of stored energy.

o ENERGY TO STORAGE (STEI) is the amount of energy, both solar
and auxiliary, delivered to the primary storage medium.

o ENERGY FROM STORAGE (STEO) is the amount of energy extracted
by the load subsystems from the primary storage medium.

A-l

o CHANGE IN STORED ENERGY (STECH) is the difference in the estimated
stored energy during the specified reporting period, as indicated
by the relative temperature of the storage medium (either posi-
tive or negative value).

o STORAGE AVERAGE TEMPERATURE (TST) is the mass-weighted average
temperature of the primary storage medium.

o STORAGE EFFICIENCY (STEFF) is the ratio of the sum of the energy
removed from storage and the change in stored energy to the
energy delivered to storage.

ENERGY COLLECTION AND STORAGE SUBSYSTEM

The Energy Collection and Storage Subsystem (ECSS) is composed of the
collector array, the primary storage medium, the transport loops between
these, and other components in the system design which are necessary to
mechanize the collector and storage equipment.

o INCIDENT SOLAR ENERGY (SEA) is the total insolation available
on the gross collector array area. This is the area of the
collector array energy-receiving aperture, including the frame-
work which is an integral part of the collector structure.

o AMBIENT TEMPERATURE (TA) is the average temperature of the out-
door environment at the site.

o ENERGY TO LOADS (SEL) is the total thermal energy transported
from the ECSS to all load subsystems.

o AUXILIARY THERMAL ENERGY TO ECSS (CSAUX) is the total auxiliary
energy supplied to the ECSS, including auxiliary energy added to
the storage tank, heating devices on the collectors for freeze-
protection, etc.

o ECSS OPERATING ENERGY (CSOPE) is the critical operating energy
required to support the ECSS heat transfer loops.

HOT WATER SUBSYSTEM

The hot water subsystem is characterized by a complete accounting of the
energy flow into and from the subsystem, as well as an accounting of
internal energy. The energy into the subsystem is composed of auxiliary
fossil fuel, and electrical auxiliary thermal energy, and the operating
energy for the subsystem.

o HOT WATER LOAD (HWL) is the amount of energy required to heat
the amount of hot water demanded at the site from the incoming
temperature to the desired outlet temperature.

A-2

o SOLAR FRACTION OF LOAD (HWSFR) is the percentage of the load
demand which is supported by solar energy

o SOLAR ENERGY USED (HWSE) is the amount of solar energy supplied
to the hot water subsystem.

o OPERATING ENERGY (HWOPE) is the amount of electrical energy
required to support the subsystem, (e.g., fans, pumps, etc.)
and which is not intended to directly affect the thermal state
of the subsystem.

o AUXILIARY THERMAL USED (HWAT) is the amount of energy supplied
to the major components of the subsystem in the form of thermal
energy in a heat transfer fluid, or its equivalent. This term
also includes the converted electrical and fossil fuel energy
supplied to the subsystem.

o AUXILIARY FOSSIL FUEL (HWAF) is the amount of fossil fuel energy
supplied directly to the subsystem.

o ELECTRICAL ENERGY SAVINGS (HWSVE) is the estimated difference
between the electrical energy requirements of an alternative
conventional system (carrying the full load) and the actual
electrical energy required by the subsystem.

o FOSSIL FUEL SAVINGS (HWSVF) is the estimated difference between
the fossil fuel energy requirements of the alternative conven-
tional system (carrying the full load) and the actual fossil
fuel energy requirements of the subsystem.

SPACE HEATING SUBSYSTEM

The space heating subsystem is characterized by performance factors account-
ing for the complete energy flow into the subsystem. The average building
temperature is tabulated to indicate the relative performance of the
subsystem in satisfying the space heating load and in controlling the tem-
perature of the conditioned space.

o SPACE HEATING LOAD (HL) is the sensible energy added to the
air in the building.

o SOLAR FRACTION OF LOAD (HSFR) is the fraction of the sensible
energy added to the air in the building derived from the solar
energy system.

o SOLAR ENERGY USED (HSE) is the amount of solar energy supplied
to the space heating subsystem.

A-3

o OPERATING ENERGY (HOPE) is the amount of electrical energy
required to support the subsystem, (e.g., fans, pumps, etc.)
and which is not intended to directly affect the thermal
state of the system.

o AUXILIARY THER M AL US ED (HAT) is the amount of energy supplied
to the major components of the subsystem in the form of thermal
energy in a heat transfer fluid or its equivalent. This term
also includes the converted electrical and fossil fuel energy
supplied to the subsystem.

o AUXILIARY ELECT RI CAL FUEL (HAE) is the amount of electrical
energy supplied directly to the subsystem.

o ELECTRICAL E NERGY SAVINGS {HSVE) is the estimated difference
between the electrical energy requirements of an alternative
conventional system (carrying the full load) and the actual
electrical energy required by the subsystem.

o BUILDING TEMPERATUR E (TB) is the average heated space dry bulb
temperature.

PASSIVE SYSTEM ENVIRONMENT

In addition to the environmental summary performance factors presented
earlier, additional performance factors describing the environment of a
passive space heating system are presented.

o BUILDING COMFORT ZONE 1 (C0M1 ) is an index relating to the com-
fort conditions on the south side of the building. The index
is formed as an average of the average dry bulb and mean radiant
temperatures inside the sone.

o BUILDING COMFORT Z ONE 2 (COM2) is an index relating to the

comfort conditions on the north side of the building and is de-
fined similarly to the other comfort index.

o BUILDING TEMPERATURE MIDNIGHT (TMID) is the average building
interior temperature at midnight local solar time.

o BUILDING TEMPERATURE 6 A.M. (T6AM) is the average building
interior temperature at 6 A.M. local solar time.

o BUILDING TEMPERATURE NOON (TNOON) is the average building interior
temperature at local solar noon.

o BUILDING TEMPERATURE 6 P.M. (T6PM) is the average building
interior temperature at 6 P.M. local solar time.

o INTERIOR RELATIVE HUMIDITY (RELHIN) is the average relative
humidity inside the building.

A-4

o AVERAGE STORAGE TEMPERATURE , (TST) is the mass weighted average
temperature of all solar storage masses.

o WIND DIRECTION (WDIR) is the average direction of the prevailing
wind.

o WIND SPEED (WIND) is the average wind speed measured at the site.

o DAYTIME AMBIENT TEMPERATURE (TDA) is the temperature during the
period from three hours before solar noon to three hours after
solar noon.

o RELATIVE HUMIDITY (RELH) is the average outside relative humidity.

A-5

APPENDIX B
SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS
LIVING SYSTEMS

INTRODUCTION

Solar energy system performance is evaluated by performing energy balance
calculations on the system and its major subsystems. These calculations
are based on physical measurement data taken from each sensor every
320 seconds. This data is then mathematically combined to determine the
hourly, daily, and monthly performance of the system. This appendix
describes the general computational methods and the specific energy
balance equations used for this site.

Data samples from the system measurements are integrated to provide
discrete approximations of the continuous functions which characterize
the system's dynamic behavior. This integration is performed by summation
of the product of the measured rate of the appropriate performance para-
meters and the sampling interval over the total time period of interest.

There are several general forms of integration equations which are
applied to each site. These general forms are exemplified as follows:
The total solar energy available to the collector Array is given by

SOLAR ENERGY AVAILABLE = (1/60) l [1001 x AREA] x At

where 1001 is the solar radiation measurement provided by the pyranometer
in Btu per square foot per hour, AREA is the area of the collector array
in square feet, Ax is the sampling interval in minutes, and the factor
(1/60) is included to correct the solar radiation "rate" to the proper
units of time.

Similarly, the energy flow within a system is given typically by

COLLECTED SOLAR ENERGY = E [Ml 00 x AH] x Ax

where Ml 00 is the mass flow rate of the heat transfer fluid in lb /min and
AH is the enthalpy change, in Btu/lb m , of the fluid as it passes through
the heat exchanging component.

For a liquid system AH is generally given by

AH = C AT
P

where C is the average specific heat, in Btu/(lb -°F), of the heat trans-
fer fluid and AT, in °F, is the temperature differential across the heat
exchanging component.

B-l

For an air system AH is generally given by

AH = H (T .) - H (T. )

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where H (T) is the enthalpy, in Btu/lb , of the transport air evaluated
at the ^nlet and outlet temperatures or the heat exchanging component.

H (T) can have various forms, depending on whether or not the humidity
rcttio of the transport air remains constant as it passes through the heat
exchanging component.

For electrical power, a general example is

ECSS OPERATING ENERGY = (3413/60) Z [EP100] x At

where EP100 is the power required by electrical equipment in kilowatts
and the two factors (1/60) and 3413 correct the data to Btu/min.

These equations are comparable to those specified in "Thermal Data
Requirements and Performance Evaluation Procedures for the National Solar
Heating and Cooling Demonstration Program." This document was prepared
by an interagency committee of the Government, and presents guidelines
for thermal performance evaluation.

Performance factors are computed for each hour of the day. Each integra-
tion process, therfore, is performed over a period of one hour. Since
long-term performance data is desired, it is necessary to build these
hourly performance factors to daily values. This is accomplished, for
energy parameters, by summing the 24 hourly values. For temperatures,
the hourly values are averaged. Certain special factors, such as effi-
ciencies, require appropriate handling to properly weight each hourly
sample for the daily value computation. Similar procedures are required
to convert daily values to monthly values.

B-2

EQUATIONS USED TO GENERATE MONTHLY PERFORMANCE VALUES

NOTE: SENSOR IDENTIFICATION (MEASUREMENT) NUMBERS REFERENCE SYSTEM
SCHEMATIC FIGURE 3-2

AVERAGE AMBIENT TEMPERATURE (°F)

TA = (1/60) x Z T001 x At

AVERAGE BUILDING TEMPERATURE (°F)

TB = (1/60) x l [(T600 + T601 + T602 + T603)/4] x At

DAYTIME AVERAGE AMBIENT TEMPERATURE (°F)

TDA = (1/360) x I T001 x At

FOR + 3 HOURS FROM SOLAR NOON

TIME OF DAY BUILDING TEMPERATURES (ONCE PER DAY)

TMID = TB

AT 12 HOURS FROM LOCAL SOLAR NOON

T6AM = TB

AT 6 HOURS BEFORE LOCAL SOLAR NOON

TNOON = TB

AT LOCAL SOLAR NOON

T6PM = TB

AT 6 HOURS PAST LOCAL SOLAR NOON

INCIDENT SOLAR ENERGY PER SQUARE FOOT (BTU/FT 2 )

SE = (1/60) x I 1002 x At

OPERATIONAL INCIDENT SOLAR ENERGY (BTU)

SEOP = (1/60) x E [1002 x (192 * (D101 + D102 + D103) + 81 (D104 + D105
+ D106))/3] x At

HUMIDITY RATIO FUNCTION (BTU/lb -°F)

HRF = 0.24 + 0.444 x HR

B-3

WHERE 0.24 IS THE SPECIFIC HEAT ANL HR IS THE HUMIDITY RATIO
OF THE TRANSPORT AIR. THIS FUNCTION IS USED WHENEVER THE
HUMIDITY RATIO WILL REMAIN TjNSTANT AS THE TRANSPORT AIR FLOWS
THROUGH A HEAT EXCHANGING DEVICE OR AS IN INFILTRATION
AVERAGE FLOOR STORAGE TEMPERATURE

TSTSLAB = (1/1200) x E (T201 + T202 + T203 + T204 + T205 +
T206 + T207 + T208 + T209 + T210 + T212 + T213 +
T214 + T215 + T217 + T218 + T219 + T220 + T221 +
T222) x At
AVERAGE WATER STORAGE TEMPERATURE

TSTST012 = (1/720) x E (T271 + T281 + T272 + T282 + T273 +
T283 + T231 i 1241 + T232 + T242 + T233 + T243)
SUM OF CONDUCTION LOSSES (U X A)

LOSSES = HTN + HTS + HTW + HTE + HFL + HRF + EDGE LOSS + HSTECH
ELECTRICAL HEAT INCIDENTLY APPLIED TO SPACE HEATING

HAE = 56.8833 * (EP600 - OUTSIDE LIGHTS - EP100)
SPACE HEATING SUBSYSTEM AUXILIARY NATURAL GAS FUEL ENERGY (BTU)

HAF = 1000 * F400
SPACE HEATING SUBSYSTEM AUXILIARY THERMAL ENERGY (BTU)

HAT = 0.52 * HAF
SPACE HEATING SUBSYSTEM LOAD (BTU)

HL = LOSSES + HI - HAE - HFIRE
INCIDENT SOLAR ENERGY ON COLLECTOR ARRAY (BTU)

SEA = CLAREA x SE

COLLECTED SOLAR ENERGY (BTU)

SEC = SECA/CLAREA

B-4

COLLECTOR ARRAY EFFICIENCY

CAREF = SECA/SEA

CHANGE IN STORED ENERGY (BTU)

STECH = WATERMASS * (TSTS012 - TSTST012 ) + 0.2 * SLABMASS *

(TSTSLAB - TSTSLAB )

WHERE THE SUBSCRIPT REFERS TO A PRIOR REFERENCE VALUE

SOLAR ENERGY TO LOAD SUBSYSTEMS (BTU)

SEL = HSE
SPACE HEATING SUBSYSTEM SOLAR FRACTION (PERCENT)

HSFR = 100 x HSE/HL
EXTERIOR RELATIVE HUMIDITY

RELH = RH001/60 x Ax
INTERIOR RELATIVE HUMIDITY

RHIN = RH600/60 x Ax
WIND NORTH - SOUTH COMPONENT

WNS = V001 * COSD (D001)/60 x Ax
WIND EAST - WEST COMPONENT

WEW = V001 x SIND (D001 )/60 x Ax
WIND VELOCITY

WIND = V001/60 x Ax
AVERAGE TEMPERATURE OF STORAGE (°F)

TST = (1/60) x I (TSTSLAB + TSTST012)/2 x Ax
SOLAR ENERGY TO SPACE HEATING SUBSYSTEM (BTU)

HSE = HL - HAT
HEAT OF INFILTRATION

HI = VOLUME x 0.07216 x HRF x (TB - TA) * HINF
WHERE HINF = AIR CHANGES PER HOUR

B-5

SPACE HEATING SUBSYSTEM FOSSIL ENERGY SAVINGS (BTU)

HSVF = HSE/0.6
SYSTEM LOAD (BTU)

SYSL = HL
SOLAR FRACTION OF SYSTEM LOAD (PERCENT)

SFR = HSFR
AUXILIARY THERMAL ENERGY TO LOADS (BTU)

AXT = HAT
AUXILIARY ELECTRICAL ENERGY TO LOADS (BTU)

AXE = N.A.
SYSTEM OPERATING ENERGY (BTU)

SYSOPE = N.A.
SYSTEM AUXILIARY FOSSIL ENERGY (BTU)

AXF = HAF
TOTAL FOSSIL ENERGY SAVINGS (BTU)

TSVF = HSVF
COMFORT INDEX ZONE 1

COM1 = ((TSTSLAB + TSTSTOl )/2 + (T604 + T605 + T606)/3)/2
COMFORT INDEX ZONE 2

COM2 = (TSTST02 + (T601 + T602 + T603)/3)/2
WIND DIRECTION

WDR = ATAN (WEW, WNS)

ADD OR SUBTRACT 360 TO GET BETWEEN AND 360°

B-6

APPENDIX C
LONG-TERM AVERAGE WEATHER CONDITIONS

This appendix contains a table which lists the long-term average weather
conditions for each month of the year for this site.

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